I agree and apparently so does the CA/B forum: SC085: Require DNSSEC for CAA and DCV Lookups is currently in intellectual property review.

DCV is CA/B speak for domain-control validation; CAA = these are my approved CAs.

This seems to be optional in the sense that: if a DNS zone has DNSSEC, then validation must succeed. But if DNSSEC is not configured it is not required.